Effect of BB drop on handling

[Clancy]

So my basic understanding is that the more BB drop, the more stable the bike is. Downside of a bike with a lot of BB drop is the potential to hit a peddle in turns. The other downside is a bike with a lot of drop is not as responsive, not as quick in turning.

I know typical is 70mm, cross bikes less, gravel bikes and endurance bikes more.

I'm sure there's a lot more to consider then that. So what are all the factors involved in BB drop when designing a frame?

For example, when looking at the geometry chart for many manufacturers I'll see 70mm of drop ( if they even show it ) for every size, 48 to 60. In my simple mind it seems that the drop on a 48 should be different then found on a 60 - but maybe not.

The other area of confusion is how aspects of handling are stated. Often times I feel I'm reading about a bottle of wine with the nebulous terms used to describe the handling. I would think that more specific and defined terms would be used so that there's a clear understanding that if measurement "X" is changed, "y' will happen. More terms common in an engineered product rather then terms used to describe the flavor of an expensive cheese.

[invertedhog]

Sounds like you already understand what needs to be understood.
Higher BB is slightly more clearance for obstacles.
Higher BB makes the bike more responsive/twitchy like true CX race bikes or crit bikes.
Lower BB drops the rider center of gravity and makes bike more stable.
BB drop should be less on larger size frames which will use longer cranks.
Drop is probably consistent from the bottom of the size range up through 55/6cm and then shorten by 5mm to accomodate the change from 170/172.5 to 175mm cranks.

[Mark McM]

So my basic understanding is that the more BB drop, the more stable the bike is. Downside of a bike with a lot of BB drop is the potential to hit a peddle in turns. The other downside is a bike with a lot of drop is not as responsive, not as quick in turning.

Can anyone explain why this should be? Raising the BB raises the CG (Center of Gravity). Raising the CG increases the angular inertia, so a bike with a higher CG should fall over more slowly, and therefore be more stable.

As an example, try balancing a broom or a map in the palm of your hand. If broomhead is at the top, the CG will be higher, and it is easier to balance. If the broomhead is at the bottom, the CG will be lower, and it is harder to keep balanced. What is different on a bike?

[benb]

CG is higher with a higher BB, as soon as the bike moves off 0 degree angle the lever arm torquing the bike to the side around the tire contact point is greater making the bike turn in faster/easier? I'm sure there is more to it than that when you add in all the other forces but I think that is the variable that changes when you change the CG.

Whatever the case it is real, it might be subtle on bicycles but ride a harley davidson and then ride a sport bike, huge difference.

[HenryA]

Imagine a line through the axles of the wheels, then add the bottom bracket spindle position in relation to that line. BB spindle below the line "hangs" or suspends the bike and rider weight. BB spindle above the line and the bike wants to fall over - the weight of the bike and rider is on top just balanced there. As soon as the balance becomes imperfect it'll tip over.

The reason that bikes of a given model in different sizes have the same BB drop is because they use the same size wheels. The weight still gets "hung" over the same wheel dimension.

[false_Aest]

Lower CG makes the bike more stable.
But I like being able to pedal through turns in a crit.
I've started to gain weight in my ankles instead of my man boobs.

[Black Dog]

Can anyone explain why this should be? Raising the BB raises the CG (Center of Gravity). Raising the CG increases the angular inertia, so a bike with a higher CG should fall over more slowly, and therefore be more stable.

As an example, try balancing a broom or a map in the palm of your hand. If broomhead is at the top, the CG will be higher, and it is easier to balance. If the broomhead is at the bottom, the CG will be lower, and it is harder to keep balanced. What is different on a bike?

The spinning wheels and lowering the centre of gravity towards the axles. the lower you go the more stable it gets.

[Mark McM]

Imagine a line through the axles of the wheels, then add the bottom bracket spindle position in relation to that line. BB spindle below the line "hangs" or suspends the bike and rider weight. BB spindle above the line and the bike wants to fall over - the weight of the bike and rider is on top just balanced there. As soon as the balance becomes imperfect it'll tip over.

The reason that bikes of a given model in different sizes have the same BB drop is because they use the same size wheels. The weight still gets "hung" over the same wheel dimension.

The bike is not "hung" from the wheel axles. If it were, a bike with small wheels would be totally unstable and fall over right away. It would also mean that bikes with different wheel sizes would require different BB heights for the same stability.

If a bike is "hung" from anywhere, it is the ground contact points.

[Mark McM]

The spinning wheels and lowering the centre of gravity towards the axles. the lower you go the more stable it gets.

That's no explanation. What does the spinning wheels have to do with it?

[Clancy]

Imagine a line through the axles of the wheels, then add the bottom bracket spindle position in relation to that line. BB spindle below the line "hangs" or suspends the bike and rider weight. BB spindle above the line and the bike wants to fall over - the weight of the bike and rider is on top just balanced there. As soon as the balance becomes imperfect it'll tip over.

The reason that bikes of a given model in different sizes have the same BB drop is because they use the same size wheels. The weight still gets "hung" over the same wheel dimension.

Best answer I've heard, super easy to picture, makes complete sense.

With your explanation, then it would be true wheelbase has no relationship to BB drop as the riders weight is still suspended the same regardless? The impact of wheelbase would be weight bias on wheels, front and rear, which would impact handling.

But that's a different topic I would guess.

[Mark McM]

Best answer I've heard, super easy to picture, makes complete sense.

With your explanation, then it would be true wheelbase has no relationship to BB drop as the riders weight is still suspended the same regardless? The impact of wheelbase would be weight bias on wheels, front and rear, which would impact handling.

But that's a different topic I would guess.

Well, except that HenryA's explaination is completely wrong. Here's a simple proof:

He claims that the BB is suspended at the axles, and that if the mass is below the axles, the bike will be stable. Try putting a large mass on the pedals, so that the CG is below the axles. Now let go of the bike to see if it is now stable. Does the bike fall over? Yep, it sure does - it is not stable.

Now get a bike with small wheels, so with the same BB height, the BB is above the axles. Put the same large mass on the pedals. When you let go of the bike, it still falls over - at exactly the same speed as the other bike, so the bike is no more or less stable. The height of the axles has no affect on bicycle stability.

[David Kirk]

There is no magic or mystical relationship between BB center and axle center at all. Full stop. The only reason we compare them and call it "BB drop" is that it makes it easier to compare bike A to bike B without the tire size factoring in. So for any given rolling diameter of tire BB height is a more accurate way to refer to it. Once you change tires all bets are off and BB drop is the ticket.

The bike doesn't 'hang from its axles' but instead stands on the contact patch of the tire. BB drop (or more accurately BB height) has only a bizarrely small relationship of the BB center to wheel axle center and only in terms of the gyroscopic action of the wheels and how far the wheels are away from the body's center of mass. It's so small it should be set aside.

The reason the 'balancing a broom' analogy doesn't fully fit is that when you balance a broom you do so by moving your hand around to keep it under the center of mass of the broom. The length of the broom makes it possible because it will allow gross movements of the hand holding it up to keep it balanced. Forget the broom and try it with a pencil - the shortness of the pencil makes it much harder demonstrating that the longer piece is easier to balance.

But a bike isn't balanced by sliding the contact patch of the tire around on the surface of the pavement.....in fact if you have a very low friction surface that will allow the contact patch to move, say ice, it's nearly impossible to keep the bike upright. If the broom analogy held water I think a slippery surface would make it easier to balance, not harder.

I think a more apt analogy might be a walker on stilts. Picture walking on short stilts....say 3 inches tall. It would be very easy and people do it all the time with high heeled shoes. Now picture a person on 6 foot stilts. It is of course much harder to maintain balance on the tall vs. the short stilts. But even this analogy falls down (pun intended) because a stilt walker maintains balance by picking up the stilt and moving it so that the stilt is on the floor directly under the walkers COG so in some ways it's like the broom deal.

In any case......if you have two bikes with two different BB heights the one with a lower BB will be more stable. If the two bikes are identical in every other way aside from BB height then they will steer 99.99% the same as long as the two BB's are within normal ranges - if you raise the BB 2 feet it will of course have a huge effect but the 10ish mm that bikes typically vary will not appreciably change the steering.

Lower BB's simply handle better...or should I say most riders prefer them. The downside of course is fear of striking a pedal on the floor and that is a big enough fear that most makers will raise the BB to give the rider more room to pedal in a corner. Pedal clearance is, IMHO, the only reason to not make the BB right down on the floor. But since one does need to pedal these things having it a bit too low is a problem and having a bit higher than needed is easy to work around......hence highish BB's on most race bikes.

Speaking of race bikes......I need to go finish one up and put it in a box - thanks for reading.

dave

[Mark McM]

The reason the 'balancing a broom' analogy doesn't fully fit is that when you balance a broom you do so by moving your hand around to keep it under the center of mass of the broom. The length of the broom makes it possible because it will allow gross movements of the hand holding it up to keep it balanced. Forget the broom and try it with a pencil - the shortness of the pencil makes it much harder demonstrating that the longer piece is easier to balance.

But a bike isn't balanced by sliding the contact patch of the tire around on the surface of the pavement.....in fact if you have a very low friction surface that will allow the contact patch to move, say ice, it's nearly impossible to keep the bike upright. If the broom analogy held water I think a slippery surface would make it easier to balance, not harder.

The broom balancing example actually does apply, because we actually do move the tire contact points side to side on the pavement in order to maintain balance. We don't do it by sliding the tires, instead we do it by steering the front wheel. This is why it is much easier to balance a bike when it is moving than when it is stopped - when the bike is moving, steering the wheel causes the wheels to move to the side. It should be remembered that bikes are not passively stable - they must be actively balanced by the actions of the rider. The riders action that keep the bike upright is continuously steering the bike to keep the ground contact point under the CG.

(By the way, this is why bikes much be countersteered - in order to start a turn, the wheels must first be steered to the opposite side, or momentarily countersteering. This steering action moves the wheels out from under the rider, creating a lean. Once the wheels are out from under us, and the bike is leaned over, the bike is brought to a stable lean by steering into the direction of the lean. The turn is finished by the steering the wheels a little sharper into the direction of the lean, to steer the wheels back under our CG.)

As far as lower BBs feeling more stable - is that in all speed domains? For example, bikes with low trail often feel quite stable at low speed, but less stable at high speed, whereas bikes with high trail can often feel unstable at low speed, but very stable at high speed.

[Rusty Luggs]

CG is higher with a higher BB, as soon as the bike moves off 0 degree angle the lever arm torquing the bike to the side around the tire contact point is greater making the bike turn in faster/easier? I'm sure there is more to it than that when you add in all the other forces but I think that is the variable that changes when you change the CG.


That is basically the explanation - force acting through longer lever arm with high CG acting to unbalance the bike. Opposite with low CG.

[TimD]

One thing I didn't notice mentioned in this thread -

A lower BB allows a lower saddle height relative to the bars for a given leg extension. For most folks this is secondary or tertiary, but if one happens to be 6'4" with a need for not much saddle-bar drop then every little bit helps.

I often smirk at geometry charts listing "XL / XXL / XXXL" frames with ~185mm HT lengths and frame stack heights of 375mm... :crap:

[Mark McM]

One thing I didn't notice mentioned in this thread -

A lower BB allows a lower saddle height relative to the bars for a given leg extension. For most folks this is secondary or tertiary, but if one happens to be 6'4" with a need for not much saddle-bar drop then every little bit helps.

I often smirk at geometry charts listing "XL / XXL / XXXL" frames with ~185mm HT lengths and frame stack heights of 375mm... :crap:

Nope. Saddle-to-bar height difference is independent of BB height (or should be, if the bike is fitted correctly).

[Black Dog]

That's no explanation. What does the spinning wheels have to do with it?

Centripetal force. Gyroscopic effect.

[Peter P.]

After riding many bikes with that "average" BB drop of 7cm, I ordered a custom frame with 8cm of drop.

Of course, I could be imagining things, but I'm inclined to say I feel the lower bottom bracket makes the bike want to stay more upright, therefore it takes a wider arc through turns. It also feels like the bike leans over only with more effort. If I consciously apply force to the outside pedal while in a turn, THEN the bike REALLY starts to do business with turning. As a result of the low BB, the bike rides a straight line with ease.

But I'm reaching to describe something that really could be my imagination, or just a way to justify my spec'ing that low BB drop in the first place.

[carpediemracing]

I'm curious about this discussion, will read the longer posts carefully later.

My challenge is that I want to either get a really short head tube, like 5 cm, maybe 4 cm, so I can use a normal stem. Or I could raise the BB a lot, like 2 cm, and use a reasonably normal looking stem. Right now I have a 9.5 cm head tube and a stem that drops 3 cm.

I have no idea what a bike would feel like with a 2 cm higher BB. I'm primarily a crit rider but I don't think I'd like a wobbly feeling bike. My only saving grace in races is to be able to sit in super effectively. If I can't ride close to other riders comfortably because the bike feels sketchy then it won't do me any good. Also if it feels sketchy in hard corners I wouldn't want it either.

[11.4]

There are a couple issues here that might get a bit more attention.

First, when talking about bike stability we're concerned about stability while riding. At that point, we have the stability induced by the spinning wheels that overwhelms any change in stability related to bottom bracket height. With the wheels spinning, it's actually hard to tip the bike over. Try riding on rollers and you can see that -- you have to steer your way into a crash to have one.

Second (and Dave Kirk, please chime in here), what creates an sensation of instability with a change of bottom bracket height really is a matter of front end flop. When a bike front end is turned to one side, the height of the front end drops. If the bottom bracket is higher, it pushes the handlebars higher if the same fit is maintained. Then when the front end flops, there's a bit more sensation of drop in the front, which at least feels like it's destabilizing, even though it really isn't. The flop causes more shift in center of gravity than a change in bottom bracket height, and it also enforces a change in CG that overrules any centripetal force created by spinning wheels.

[11.4]

And I don't think anyone's mentioned it, but a 3-6 mm difference in CG height? A slight difference in position can change CG more than that.

And the equation becomes more complex when considering bikes like cross or gravel bikes with longer fork blades. Such bikes have different flop geometries.

[marciero]

Is easy to see that lower CG is more stable by considering the extreme of CG below the contact patch. You could do this in practice by putting a bike on an elevated rail or wire/tightrope with curved balancing pole with weights below the wire. I'm sure I can recall some kind of circus act actually doing this. As long as the steerer is locked in place (not turning due to wheel flop, eg.) the bike will stay balanced, stationary, by itself, and in fact will right itself if pushed over.

The broom handle comparison is interesting...
With the higher CG/broom at the top it is indeed easier to balance since the greater inertia causes it to fall over more slowly, giving you more time to react and balance. But note also that greater hand movements are needed to correct and balance. With the lower CG/broom at bottom, is difficult to balance but requires smaller hand corrections.

I dont think any of this plays out in practice with the small differences we are talking about. I think, as David Kirk mentions, it's more about the handling.

[Ronsonic]

The tire patch is the pivot point of the bike's lateral roll movements, the fulcrum. The closer to it the less leverage the center of gravity has on the rest.
That makes for more stability, the rider is the most disruptive thing there. The rest is intrinsically stable.

A lot of bike steering involves weight shifting and counter-steer rather than turning the bars in the direction you want to go. That is definitely going to be affected.

The lower bottom bracket will move slightly less over bumps.

I like my gravel bike, lowish bracket and a quick front-end.

[HenryA]

MarkMcM,

For someone who asked a question early on and then poo-pooed all the answers, I must ask: was your question real or just a lure to invite comments for you to criticize?

Otherwise, please notice my post started with the word "Imagine".

[steamer]

The location of the COG is all that is affected by raising or lowering the BB. Its a minor effect and is overshadowed by lots of other factors. All else is placebo.

[HenryA]

Ronsonic wrote:

"the rider is the most disruptive thing there"

Good comment.

Rider weight distribution on saddle and pedals has loads to do with BB drop and the feeling of stability. When standing on pedals versus sitting on seat the COG of the system changes a lot. Lots of levers involved kinda as in Dave Kirk's description - the guy on stilts.

Its mostly about how the rider's weight is carried by the bike. Rider being about 8-10 times the weight of the bike.

Imagine (theres that word again) riding a kids scooter that has a platform to stand on that is 3 inches off the ground versus another 3 feet off the ground. All else being equal, which would be easier to balance on?

[fuzzalow]

My approach towards cycling is always predicated on the variables imposed by the rider and virtually never on the millimeters and minutiae of bicycle frame measurements and geometry. It is easy to take a good bike and screw it up with a bad fit.

Nobody can feel or pick out the difference in 10mm or less difference in BB drop from one frame to the next. The handling differences exist on paper but not as something in real life that a rider's mass, positioning and movement on the bike won't overshadow to turn BB drop into a meaningless number.

These talks conflate the techy-talk of bike geometry, which exists on paper and is real, with rider perceptions, based on expectation and nothing else of what those numbers should mean when riding it. The rider perception part isn't real, but it has the effect of it's being whatever you want it to feel and be.

I can answer the OP question on the effect of BB drop on handling: it can effect the ability to dial in a fit & position because a lower BB reduces the amount of maximum available bar drop that can be setup into that frame. And not being able to get a balanced result into a rider's fit & position will effect the ride & handling of how the rider uses that particular bike.

[Joxster]

1697922411

Now thats a low centre of gravity ;)

[Bob Ross]

A half dozen years or so ago Tom Kellogg wrote this across the hall:

"What I am talking about is the perceived difference in the way that two, otherwise identical bikes will accelerate when the only difference between the two bikes is the BB drop difference of, say 6mm. The lower BB bike will feel as though it is "more willing" to accelerate when the rider is standing. This applies to situations where a rider is jumping out a corner, leaving an intersection or climbing out of the saddle. The perception pretty much goes away once the rider is back in the saddle. What is going on here are a couple of things.

First, the obvious one; when a bottom bracket is lower, the entire bike is lower, everything. Not just the BB and seat tube, but top tube, saddle, bars ... all of the weight of the bike is lower. Since a bike "rocks" around the fulcrum point of the contact patch of the tires, the closer the structure of the bike is to that point, the less force is required to rock the bike, it feels as though there is less bike fighting the rider.

Second, and this one is hard for me to communicate, since I really don't understand fully how it works from a bio-mechanical perspective. When a rider stands up to accelerate, usually, there is some degree of rocking motion that the bike goes through. The lower the BB, the less lateral movement the BB and cranks make during a rocking cycle. Bikes with very high bottom brackets keep the riders pedals farther away from the ground and the rocking fulcrum, therefore making for more lateral movement of the BB during rocking. At the same time, downward pedaling forces during rocking have a tendancy to add to the rocking motion. But the higher the BB, the more those forces will add to that motion. Lower bottom brackets have less effect on the natural motion since those BBs are closer to the rocking fulcrum and don't "rock" as far. With the higher bottom brackets, the rider needs to compensate more for the pedaling forces and the bike seems to take more upper body effort to ride naturally, or neutrally. "

[tigoat]

Nope. Saddle-to-bar height difference is independent of BB height (or should be, if the bike is fitted correctly).

No, BB drop (or height) affects the saddle height directly so it is part of the saddle to bar drop relationship.

[tigoat]

It makes my head hurt when I have to think about all the physics of BB drop vs. handling that are being discussed here so I am not gonna go into that just for the sake of debating. I will say though having a higher BB position (within reason) can be a good thing for some riders. I have a bike with a 40mm BB drop, which is very high, and it rides like a dream. If you don’t believe me, just ask Jim Kish about it. The major reason I wanted it that high was due to the amount of saddle to bar drop I desired, as the BB drop effects my saddle height directly. I didn’t even care about the handling that could be caused by a higher BB position when I designed this bike but it turned out to be just great. I didn’t notice any negative effects on handling, as this bike tracks solidly and corners quickly. What I noticed was I was going down a hill much faster with this bike than with my other bikes that have a BB drop of 70mm. Most experts in this circle seem to like the BB drop to be as low as possible and there is nothing wrong with that, but there is also nothing wrong with raising the BB higher if it is needed.

[carpediemracing]

No, BB drop (or height) affects the saddle height directly so it is part of the saddle to bar drop relationship.

Note that BB drop/height only affects saddle height if you make the BB change while making the seat tube longer and/or raising the saddle.

If you take a given length of seat tube and a given amount of seat post extension, where you plant the seat tube (i.e. the BB) doesn't affect the length of the seat tube or the post extension.

It's only if you alter the seat tube or the post extension that saddle height changes.

BB drop does affect saddle to bar position in that a higher BB would raise the saddle effective to the bars, if the head tube/stem/bars don't change. This is because if you raise the BB and do NOT raise the head tube the same amount then the bars will end up lower.

[e-RICHIE]

No, BB drop (or height) affects the saddle height directly so it is part of the saddle to bar drop relationship.


??

The change doesn't affect saddle height at all, unless you're measuring it from the ground rather than as a contact point from the central movement to the top of the depressed area on its surface. Reach and drop are also untouched. If you keep all measurements on a bicycles design the same, and only change the drop spec, the only differences will be where the bottom of the head tube is (it'll be shorter as drop increases) and the length of the down tube as it travels from the bottom bracket to its mating place on the head tube. That the head the changes from its lower side has no bearing upon 'bar drop relationship.

[bironi]

Thanks for the good thread. I've been wondering about some of this as I switch back and forth between bikes with somewhat high bb and typical race bike bb. My experience aligns well with Mr. Kellogg's description.

[Mark McM]

MarkMcM,

For someone who asked a question early on and then poo-pooed all the answers, I must ask: was your question real or just a lure to invite comments for you to criticize?

Otherwise, please notice my post started with the word "Imagine".

I asked the question because I'm genuinely interested in knowing the answer. Unfortunately, many of the first responses merely repeated many of the myths and folklore about bike stability that have long been discredited**, so my responses were merely trying to stop those lines of discussion.

However, there have been a few ideas that seem worth exploring. In my mind, I had over-simplified the bike/rider system, and considered it as one rigid mass. But obviously that is not the case - the rider can move around on the bike, particularly when out of the saddle.

For example, when we ride out of the saddle, we naturally rock the bike laterally, in order to get better alignment between our CG, the pedal we are standing on, and the ground contact point. Curiously, the lower the BB, the greater the angle we need to lean the bike to get this alignment. But on the other hand, with the lower BB we also have a larger leverage ratio when we do this (the leverage ratio in this case is the distance from the ground to the handlebars, divided by the distance from the ground to the pedals, with the ground contact being the fulcrum).

In any case, I also agree with some other commenters, that preferred BB height might largely depend on what we are used to, and that we can get used to a variety of different BB heights if we ride them long enough.

And, of course, the affect of BB height doesn't occur in a vacuum - it interacts with all the other dynamic system variables (some from the bike, and some from the rider). Take MTB bikes - while there are many geometry differences between a road bike and an MTB bike, it is interesting to note that an MTB (with appropriate) tires) can feel very stable on the road, even though the BB height on the MTB might be 3 - 5 cm higher than on a typical road bike.



**The Wikipedia article on cycle stability dynamics (https://en.wikipedia.org/wiki/Bicycle_and_motorcycle_dynamics) is a good place to start, and has about 50 references for further reading. This article dispels many of the common myths about bicycle stability, in particular about things like countersteering and gyroscopic effects.

[aingeru]

http://davesbikeblog.squarespace.com/blog/2007/2/21/bottom-bracket-height.html

[tigoat]

In my case, my head tube was already shortest possible and it couldn’t go any shorter before the headset running into the taper section of the fork on the inside. So with this front end fixed and with a handlebar and stem picked, my saddle to bar drop(vertical height) was still 30mm short, so I raised the BB height (less drop) by 30mm from 70mm drop to 40mm get that distance to around 6.5” and it did work out just as intended. I do not have BikeCAD but you could easily replicate what I did in BikeCAD.

??

The change doesn't affect saddle height at all, unless you're measuring it from the ground rather than as a contact point from the central movement to the top of the depressed area on its surface. Reach and drop are also untouched. If you keep all measurements on a bicycles design the same, and only change the drop spec, the only differences will be where the bottom of the head tube is (it'll be shorter as drop increases) and the length of the down tube as it travels from the bottom bracket to its mating place on the head tube. That the head the changes from its lower side has no bearing upon 'bar drop relationship.

[carpediemracing]

In my case, my head tube was already shortest possible and it couldn’t go any shorter before the headset running into the taper section of the fork on the inside. So with this front end fixed and with a handlebar and stem picked, my saddle to bar drop(vertical height) was still 30mm short, so I raised the BB height (less drop) by 30mm from 70mm drop to 40mm get that distance to around 6.5” and it did work out just as intended. I do not have BikeCAD but you could easily replicate what I did in BikeCAD.

Can you post a picture of your bike? The original posts (I searched) have links that are no longer good.

I'm in a similar situation. My fix right now is to use a -32 deg stem to drop the bars 3 cm. My second bike has the original non-compact bars but I really like the compact bars I have on my main bike. To replicate the position/handling on the second bike I'd need to get another -32 deg stem.

However I'd consider a higher BB frame if it didn't adversely affect handling.

To be frank a second stem would cost less than a new frame. Still, the idea of being able to use a normal stem and be able to make minor adjustments by swapping out stems appeals to me. With a custom stem I really have no way of trying a 1 cm longer stem or a few degrees different angle.

[tigoat]

I had a PC problem while back and can no longer find a picture of that particular bike. However, I have had many other custom bikes made since then.

Here is one of them:

http://i1048.photobucket.com/albums/s365/mingbogo/CWbike_zps5iactx4u.jpg

It is hard to tell from the angle of the picture but with a higher BB position the angle of the chain stays is much shadower because the BB is closer to the horizontal line of the two wheel axles. As mentioned before, with a BB drop of 40mm, it still rides like a dream, and this particular bike is very dear to my heart. This bike just shows we can pretty much throw some of the negative theories of high BB drop from some of these "experts" out of the window. I usually don't go by what others say regardless how good it sounds, I only trust with whatever proven to work for me personally in the field.


Can you post a picture of your bike? The original posts (I searched) have links that are no longer good.

I'm in a similar situation. My fix right now is to use a -32 deg stem to drop the bars 3 cm. My second bike has the original non-compact bars but I really like the compact bars I have on my main bike. To replicate the position/handling on the second bike I'd need to get another -32 deg stem.

However I'd consider a higher BB frame if it didn't adversely affect handling.

To be frank a second stem would cost less than a new frame. Still, the idea of being able to use a normal stem and be able to make minor adjustments by swapping out stems appeals to me. With a custom stem I really have no way of trying a 1 cm longer stem or a few degrees different angle.

[carpediemracing]

Thanks. I can't do a frame right now but for me it may be worth an experiment frame if/when I can spend the money to do such an experiment.

[trentschler]

I have a couple of Moultons that don't have any bottom bracket drop at all! Because of their small wheels, the bottom bracket is above the axles. Yet they are very stable, track and descend well, don't wander and turn easily. So, a few millimeters of bottom bracket drop won't have nearly the effect on handling that head tube angle and fork offset will, nor smooth out the ride like long chainstays and a long wheelbase. I have an older Klein Quantum (racing bike) and a Klein Performance (touring bike) and about the only difference between the two is a slacker head angle and longer chainstays on the Performance. But it's a much smoother ride and not as quick to turn.

The Moultons do have surprising long wheelbases but they're still pretty compact because of the small wheels.